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Fencer Vulns
high 7.4

CVE-2020-13777 in the critical feed json

GnuTLS 3.6.x before 3.6.14 uses incorrect cryptography for encrypting a session ticket (a loss of confidentiality in TLS 1.2, and an authen…

published 2020-06-04 6 y ago modified 2026-10-14 26 d ago also EUVD-2020-5994 , JLSEC-2026-518

cvss
7.4
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
22.5%
EPSS 22.5% chance of exploitation in 30 days, percentile 97%
public exploits
0
none known

Summary

GnuTLS 3.6.x before 3.6.14 uses incorrect cryptography for encrypting a session ticket (a loss of confidentiality in TLS 1.2, and an authentication bypass in TLS 1.3). The earliest affected version is 3.6.4 (2018-09-24) because of an error in a 2018-09-18 commit. Until the first key rotation, the TLS server always uses wrong data in place of an encryption key derived from an application.

Patch / fix

  • julia GnuTLS_jll 3.7.1+0
  • Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP V3.1.5
  • Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP V3.1.5
  • Siemens SIPLUS S7-1500 CPU 1518-4 PN/DP MFP V3.1.5
  • gnutls28 Debian 14, Debian 13, Debian 12 3.6.14-1

debian advisories DEBIAN-CVE-2020-13777

  • gnutls28 Ubuntu 20.04 LTS 3.6.13-2ubuntu1.1

ubuntu advisories UBUNTU-CVE-2020-13777

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • gnutls RHEL 8 3.6.8-11.el8_2
  • gnutls-c++ RHEL 8 3.6.8-11.el8_2
  • gnutls-dane RHEL 8 3.6.8-11.el8_2
  • gnutls-utils RHEL 8 3.6.8-11.el8_2
  • gnutls RHEL 8.0 E4S 3.6.5-3.el8_0
  • gnutls-c++ RHEL 8.0 E4S 3.6.5-3.el8_0
  • gnutls-dane RHEL 8.0 E4S 3.6.5-3.el8_0
  • gnutls-utils RHEL 8.0 E4S 3.6.5-3.el8_0

red hat advisories RHSA-2020:2639RHSA-2020:2638RHSA-2020:2637

  • gnutls SLES for SAP 15, SLES 15-LTSS, SLE Module for Basesystem 15 SP1 +2 more 3.6.7-6.29.1

suse advisories SUSE-SU-2020:1584-1

  • gnutls openSUSE Tumbleweed 3.7.2-1.2
  • gnutls openSUSE Leap 15.1 3.6.7-lp151.2.18.1

opensuse advisories openSUSE-SU-2024:10801-1openSUSE-SU-2020:0790-1

  • gnutls Alpine 3.24, Alpine 3.23, Alpine 3.22 +13 more 3.6.14-r0

alpine advisories ALPINE-CVE-2020-13777

Alpine secdb © Alpine Linux, from https://secdb.alpinelinux.org via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • gnutls Arch Linux 3.6.14-1

arch linux advisories AVG-1177

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2020-13777 updated cvss 7.4

gnutls: session resumption works without master key allowing MITM

  • Red Hat Enterprise Linux AppStream (v. 8) gnutls-c++ 3.6.8-11.el8_2, gnutls-dane 3.6.8-11.el8_2, gnutls-utils 3.6.8-11.el8_2
    fixed: vendor fix “There's no available mitigation for this issue.” RHSA-2020:2637
  • Red Hat Enterprise Linux AppStream E4S (v. 8.0) gnutls-c++ 3.6.5-3.el8_0, gnutls-dane 3.6.5-3.el8_0, gnutls-utils 3.6.5-3.el8_0
    fixed: vendor fix “There's no available mitigation for this issue.” RHSA-2020:2639
  • Red Hat Enterprise Linux AppStream EUS (v. 8.1) gnutls-c++ 3.6.8-9.el8_1, gnutls-dane 3.6.8-9.el8_1, gnutls-utils 3.6.8-9.el8_1
    fixed: vendor fix “There's no available mitigation for this issue.” RHSA-2020:2638
  • Red Hat Enterprise Linux BaseOS (v. 8) gnutls 3.6.8-11.el8_2
    fixed: vendor fix “There's no available mitigation for this issue.” RHSA-2020:2637
  • Red Hat Enterprise Linux BaseOS E4S (v. 8.0) gnutls 3.6.5-3.el8_0
    fixed: vendor fix “There's no available mitigation for this issue.” RHSA-2020:2639
  • Red Hat Enterprise Linux BaseOS EUS (v. 8.1) gnutls 3.6.8-9.el8_1
    fixed: vendor fix “There's no available mitigation for this issue.” RHSA-2020:2638
  • Red Hat Enterprise Linux 5 gnutls Red Hat Enterprise Linux 6 gnutls, gnutls-guile, gnutls-utils Red Hat Enterprise Linux 7 gnutls, gnutls-c++, gnutls-dane, gnutls-utils
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

cisa ICSA-23-348-10 updated cvss 7.4

Siemens SIMATIC S7-1500

  • Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AB0) >= 3.1.0, < 3.1.5 Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AC0) >= 3.1.0, < 3.1.5 Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP (6ES7518-4FX00-1AB0) >= 3.1.0, < 3.1.5 Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP (6ES7518-4FX00-1AC0) >= 3.1.0, < 3.1.5 Siemens SIPLUS S7-1500 CPU 1518-4 PN/DP MFP (6AG1518-4AX00-4AC0) >= 3.1.0, < 3.1.5
    affected: fixed in V3.1.5, mitigation support.industry.siemens.com

Facts from CISA's republication of the vendor's own advisory (CSAF); the linked advisory is the authoritative source. CISA notification · csaf

Exploit prediction

22.45% chance of exploitation in the next 30 days, higher than 97% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
NVD 3.1 7.4 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N
NVD 2.0 5.8 AV:N/AC:M/Au:N/C:P/I:P/A:N
OSV 3.1 7.4 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N

Affected packages

ecosystem package affected fixed in
julia GnuTLS_jll
<3.7.1+0
3.7.1+0

Affected products

  • Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP
  • Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP
  • Siemens SIPLUS S7-1500 CPU 1518-4 PN/DP MFP

Classification

Weakness
  • CWE-327 Use of a Broken or Risky Cryptographic Algorithm

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.